The present invention relates generally to the art of compressing a gas. More particularly, the present invention relates to the compression of a refrigerant gas into which a liquid is injected during the compression process.
With still more particularity, this invention relates to the requirement to separate entrained injected oil from the oil-gas mixture discharged from a screw compressor in a refrigeration system.
Compressors are used in refrigeration systems to raise the pressure of a refrigerant gas from a suction to a discharge pressure thereby permitting the refrigerant to be used within the circuit to cool a desired medium. Many types of compressors, including rotary screw compressors, are employed to compress the refrigerant gas in a refrigeration system.
In a screw compressor two complimentary rotors are located in a housing having a low pressure end, which defines a suction port, and a high pressure end, which defines a discharge port. Refrigerant gas at suction pressure enters the low pressure end of the compressor housing and is there enveloped in a pocket formed between the counter-rotating screw rotors.
The volume of the gas pocket decreases and the pocket is circumferentially displaced as the compressor rotors rotate and mesh. The gas within such a pocket is compressed and heated by virtue of the decreasing volume in which it is contained prior to the pocket's opening to the discharge port. The pocket, as it continues to decrease in volume, eventually opens to the discharge port in the high pressure end of the compressor housing and the compressed gas is discharged from the compressor.
Screw compressors used in refrigeration applications will, in the large majority of instances, include an oil injection feature. Oil is injected, in relatively large quantity, into the working chamber of a screw compressor (and therefore into the refrigerant gas being compressed therein) for several reasons. First, the injected oil acts to cool the refrigerant gas undergoing compression. As a result, the compressor rotors are likewise cooled allowing for tighter tolerances between the rotors.
Second, the oil acts as a lubricant. One of the two rotors in the screw compressor is typically driven by an external source, such as an electric motor, with the other rotor being driven by virtue of its meshing relationship with the externally driven rotor. The injected oil prevents excessive wear between the driving and driven rotors. The oil is additionally delivered to various bearing surfaces within the compressor for lubrication purposes.
Finally, oil injected into the working chamber of a screw compressor acts as a sealant between the meshing rotors and between the rotors and the working chamber in which they are housed for the reason that there are no discrete seals in a screw compressor between the individual rotors or between the rotors and the rotor housing. Absent the injection of oil, significant leakage paths would exist internal of the compressor which would be detrimental to compressor efficiency. Oil delivery and injection therefore both increases the efficiency and prolongs the life of a screw compressor.
Oil making its way into the working chamber of a screw compressor is, for the most part, atomized and becomes entrained in the refrigerant undergoing compression. Such oil, to a great extent, must be removed from the oil-rich mixture discharged from the compressor in order to make the oil available for reinjection into the compressor for the purposes enumerated above. Further, removal of excess oil from the compressed refrigerant gas must be accomplished to ensure that the performance of the refrigerant gas is not unduly affected within the refrigeration system by the carrying of an excess amount of oil into and through system heat exchangers.
The need therefore continues to exist for reliable and efficient oil separation apparatus for screw compressor refrigeration systems which removes a predetermined and required amount of oil from the oil-refrigerant gas mixture discharged by the compressor.